1. Field of the Invention
The present invention relates to a device for detecting malfunctions of a fuel evaporative purge system provided for emission control of an internal combustion engine, more particularly to a device for a system provided with a canister for absorbing and temporarily storing a fuel vapor, such as gasoline vapor, caused by an evaporation of fuel held, for example, in a fuel tank or a carburetor; the system separating the fuel vapor from an absorbent contained in the canister and supplying same to the combustion chambers of the engine, to be burnt therein.
2. Description of the Related Art
In the conventional fuel evaporative purge system, a driver cannot be made aware of a malfunction of the purging mechanism from the canister until a periodical inspection of the engine is carried out. Therefore, if a malfunction occurs whereby the fuel vapor cannot be purged into the intake pipe, the absorbent contained in the canister will become saturated, and thus fuel vapor from, for example, the fuel tank, will not be absorbed by the absorbent but will flow directly into the atmosphere through an air inlet of the canister.
To prevent this flow of fuel vapor into the atmosphere, a device for detecting a malfunction of the purge system is disclosed in which a fuel vapor sensor is provided at an air inlet of the canister for detecting a flow of fuel vapor through the air inlet to the atmosphere, and a malfunction of the purging mechanism of the system is detected by signals output from the sensor (Japanese Unexamined Utility Model Publication No. 57-171169).
In the above device, however, since the malfunction of the purging mechanism is first detected when the absorbent is saturated and cannot absorb any more fuel vapor, a time lag occurs between a time at which the purging mechanism malfunctions and a time at which the malfunction is detected, depending upon the absorption capability of the absorbent, and thus a warning that a malfunction has occurred is delayed.
Further, in this device, if the fuel vapor cannot be purged to the intake pipe during normal driving conditions because of a malfunction of the system, a large quantity of fuel vapor which has not been absorbed in the absorbent may escape into the atmosphere when the fuel tank is filled with fresh fuel.